DENVER — Few people other than his teammates noticed problems when Broncos safety Rahim Moore left the biggest game of the season and didn’t come back Sunday night.

“He didn’t have the acceleration to make the tackle and that’s when I knew something was bothering him,” said teammate Chris Harris.

Hours later, pain woke Moore in the middle of the night and his trainer rushed him to the hospital. The diagnosis was lateral compartment syndrome.

He underwent emergency surgery early Monday.

“Compartment syndrome develops over time. It’s not like a light switch where you either have it or you don’t,” said University of Colorado’s Dr. Jason Stoneback.

He says the condition begins with any injury to the leg. For Moore, Stoneback says it was likely a football hit. He says when the tissue swells, there is no room in the surrounding compartments of the leg to expand.

“The muscle becomes squeezed as well as the vessels and nerves in that compartment and it leads to excruciating pain and possibly muscle death,” Stoneback said.

“It could have been something that started during the week. It could have been something that started during pregame warm ups. I don’t know. I’m not sure anyone knows,” Broncos interim coach Jack Del Rio said. “But at some point he ended up with basically a muscle that was bleeding. That’s the best way I can I explain it – that’s my understanding of it.”

The time frame for Moore’s return to the playing field is unknown.

As for symptoms, Stoneback said parents should look for a firm leg and pain that is disproportional from the injury that caused it.